CLEANUP: acl: cleanup some of the redundancy and spaghetti after last fix

This code aims at clearing up the ACL parsing code a bit to make it
more obvious what happens in the case of an ACL keyword and what happens
in the case of a sample expression. Variables prev_type and cur_type were
merged, and ACL keyword processing functions are checked only once.

This patch could be backported into 1.5 after the previous patch, in order
to keep the code more maintainable.
(cherry picked from commit aa4e32e10a126ad8370551c9ce0c65882f59d6bc)
diff --git a/src/acl.c b/src/acl.c
index 3e04874..8f3fd9e 100644
--- a/src/acl.c
+++ b/src/acl.c
@@ -145,7 +145,6 @@
 	const char *begw;
 	const char *endw;
 	const char *endt;
-	unsigned long prev_type;
 	int cur_type;
 	int nbargs;
 	int operator = STD_OP_EQ;
@@ -231,11 +230,9 @@
 		/* look for the begining of the converters list. Those directly attached
 		 * to the ACL keyword are found just after <arg> which points to the comma.
 		 * If we find any converter, then we don't use the ACL keyword's match
-		 * anymore but the one related to the converter's output type, so we'll
-		 * kill the ACL kw to avoid any future reference to it (since in fact we'll
-		 * only be using it as a sample fetch function).
+		 * anymore but the one related to the converter's output type.
 		 */
-		prev_type = smp->fetch->out_type;
+		cur_type = smp->fetch->out_type;
 		while (*arg) {
 			struct sample_conv *conv;
 			struct sample_conv_expr *conv_expr;
@@ -294,13 +291,13 @@
 			}
 
 			/* If impossible type conversion */
-			if (!sample_casts[prev_type][conv->in_type]) {
+			if (!sample_casts[cur_type][conv->in_type]) {
 				memprintf(err, "ACL keyword '%s' : conv method '%s' cannot be applied.",
 					  aclkw->kw, ckw);
 				goto out_free_smp;
 			}
 
-			prev_type = conv->out_type;
+			cur_type = conv->out_type;
 			conv_expr = calloc(1, sizeof(struct sample_conv_expr));
 			if (!conv_expr)
 				goto out_free_smp;
@@ -353,15 +350,9 @@
 			memprintf(err, "%s in ACL expression '%s'", *err, *args);
 			goto out_return;
 		}
-		prev_type = smp_expr_output_type(smp);
+		cur_type = smp_expr_output_type(smp);
 	}
 
-	/* From now on, prev_type is the expression's output type.
-	 * Stop relying on ACL keyword if a converter is used.
-	 */
-	if (acl_conv_found)
-		aclkw = NULL;
-
 	expr = (struct acl_expr *)calloc(1, sizeof(*expr));
 	if (!expr) {
 		memprintf(err, "out of memory when parsing ACL expression");
@@ -370,38 +361,26 @@
 
 	pattern_init_head(&expr->pat);
 
-	expr->kw = aclkw ? aclkw->kw : smp->fetch->kw;
-	expr->pat.parse = aclkw ? aclkw->parse : NULL;
-	expr->pat.index = aclkw ? aclkw->index : NULL;
-	expr->pat.match = aclkw ? aclkw->match : NULL;
-	expr->pat.delete = aclkw ? aclkw->delete : NULL;
-	expr->pat.prune = aclkw ? aclkw->prune : NULL;
-	expr->pat.expect_type = prev_type;
-	expr->smp = smp;
-	smp = NULL;
-
-	/* Fill NULL pointers with values provided by the pattern.c arrays */
-	if (aclkw) {
-		if (!expr->pat.parse)
-			expr->pat.parse = pat_parse_fcts[aclkw->match_type];
-
-		if (!expr->pat.index)
-			expr->pat.index = pat_index_fcts[aclkw->match_type];
+	expr->pat.expect_type = cur_type;
+	expr->smp             = smp;
+	expr->kw              = smp->fetch->kw;
+	smp = NULL; /* don't free it anymore */
 
-		if (!expr->pat.match)
-			expr->pat.match = pat_match_fcts[aclkw->match_type];
-
-		if (!expr->pat.delete)
-			expr->pat.delete = pat_delete_fcts[aclkw->match_type];
-
-		if (!expr->pat.prune)
-			expr->pat.prune = pat_prune_fcts[aclkw->match_type];
+	if (aclkw && !acl_conv_found) {
+		expr->kw = aclkw->kw;
+		expr->pat.parse  = aclkw->parse  ? aclkw->parse  : pat_parse_fcts[aclkw->match_type];
+		expr->pat.index  = aclkw->index  ? aclkw->index  : pat_index_fcts[aclkw->match_type];
+		expr->pat.match  = aclkw->match  ? aclkw->match  : pat_match_fcts[aclkw->match_type];
+		expr->pat.delete = aclkw->delete ? aclkw->delete : pat_delete_fcts[aclkw->match_type];
+		expr->pat.prune  = aclkw->prune  ? aclkw->prune  : pat_prune_fcts[aclkw->match_type];
 	}
 
 	if (!expr->pat.parse) {
-		/* some types can be automatically converted */
-
-		switch (prev_type) {
+		/* Parse/index/match functions depend on the expression type,
+		 * so we have to map them now. Some types can be automatically
+		 * converted.
+		 */
+		switch (cur_type) {
 		case SMP_T_BOOL:
 			expr->pat.parse = pat_parse_fcts[PAT_MATCH_BOOL];
 			expr->pat.index = pat_index_fcts[PAT_MATCH_BOOL];
@@ -440,7 +419,6 @@
 	}
 
 	/* Additional check to protect against common mistakes */
-	cur_type = smp_expr_output_type(expr->smp);
 	if (expr->pat.parse && cur_type != SMP_T_BOOL && !*args[1]) {
 		Warning("parsing acl keyword '%s' :\n"
 		        "  no pattern to match against were provided, so this ACL will never match.\n"